1. Field of the Invention
The present invention relates to an illuminating optical apparatus and a projecting optical apparatus in which the illuminating optical apparatus is employed.
2. Description of the Related Art
As an illuminating optical apparatus used for a liquid crystal projector 8, there has been conventionally provided, for example, what is shown in FIG. 1a, in which there is installed an optical integrator that is constituted by a first lens array 20 and a second lens array 22. In this illuminating optical apparatus, a light beam emitted from a light source 12 such as a metal halide lamp, is reflected by a reflector 13 so that the light beam is directed toward a liquid crystal panel 46. The first lens array 20 has a plurality of lens cells 20a each of which has an aperture generally similar in shape to the liquid crystal panel 46, as shown in FIG. 2. The first lens array 20 divides the light beam reflected by the reflector 13 into the number of light beams corresponding to the number of the lens cells 20a. On the other hand, the second lens array 22 has a plurality of lens cells 22a the number of which is the same as the number of the lens cells 20a of the first lens array 20, as shown in FIG. 3. Each of the light beams divided by the lens cells 20a of the first lens array 20 is respectively converged by each of the lens cells 22a of the second lens array 22. That is, the light source 12 and the second lens array 22 have a conjugate relation therebetween. The light source 12 has a light emitting portion that is elongate in a direction of its optical axis, so that the corresponding elongate light source images 12s are formed radially in the second lens array 22, as shown in FIG. 3. The lens cells 22a of the second lens array 22 optically project the corresponding apertures of the lens cells 20a of the first lens array 20 onto the liquid crystal panel 46 via a superposition lens 23 that is mounted near the second lens array 22 on a side of the liquid crystal panel 46. The optically projected images of the light source 12 are superposed, or overlapped, one on another, so that the liquid crystal panel 46 is illuminated uniformly.
By the way, although only one liquid crystal panel 46 is shown in FIG. 1, there are mounted three liquid crystal panels 46, actually. Also, there is mounted an unshown color separation system between the superposition lens 23 and the liquid crystal panel 46, so that each of red-, green- and blue-colored components separated by the color separation system correspondingly illuminates each of the three liquid crystal panels 46, respectively.
In case the light source images 12s formed at the lens cells 22a of the second lens array 22 are larger than the lens cells 22a so that the light source images 12s overflow the lens cells 22a (i.e. so that the light source images 12s exist beyond the lens cells 22a), the overflowing portions of the light source images 12s are not projected toward the liquid crystal panel 46. This results in a loss of the amount of light.
The size, or dimension, of the light source image 12s is inversely proportional to the focal length of the reflector 13. Therefore, in order to make efficient use of the light beam coming from the light source 12 without loss of the amount of light, it is preferable to set the focal length of the reflector 13 so that the light source image 12s is within the region of the lens cell 22a with respect to a direction of a shorter side of the lens cell 22a of the second lens array 22. Conventionally, the focal length of the reflector 13 has been set equally over the entire length of the reflector 13, in this way.
According to the setting of the focal length of the reflector 13, however, the focal length, particularly in a direction of the longer side of the lens cell 22a, becomes too long; therefore, the light source image 12s becomes smaller than necessary relative to the lens cell 22a. On this account, the illumination becomes nonuniform in the direction of the longer side of the lens cell 22a, resulting in deterioration of efficiency for illumination.
Also, the reflector 13 increases in size in proportion to its focal length. Therefore, the reflector 13 becomes larger than necessary relative to the direction of the longer side of the lens cell 22a of the second lens array, resulting in inefficient use of space therein.